President Obama said during a press conference Tuesday that the use of chemical weapons in Syria could be a “game changer” in the U.S. response to the conflict, but he made clear his administration first needs more evidence. (The Washington Post)

President Obama is preparing to send lethal weaponry to the Syrian opposition and has taken steps to assert more aggressive U.S. leadership among allies and partners seeking the ouster of President Bashar al-Assad, according to senior administration officials.

The officials said they are moving toward the shipment of arms but emphasized that they are still pursuing political negotiation. To that end, the administration has launched an effort to convince Russian President Vladimir Putin that the probable use of chemical weapons by the Syrian government — and the more direct outside intervention that could provoke — should lead him to reconsider his support of Assad.

But Obama, who spoke by telephone with Putin on Monday and is sending Secretary of State John F. Kerry to Moscow in the coming days, is likely to make a final decision on the supply of arms to the opposition within weeks, before a scheduled meeting with Putin in June, the officials said.

Confirmation that the Assad government has used chemical weapons, Obama said Tuesday, would mean that “there are some options that we might not otherwise exercise that we would strongly consider.”

At a news conference, he emphasized the need to “make sure I’ve got the facts. . . . If we end up rushing to judgment without hard, effective evidence, we can find ourselves in a position where we can’t mobilize the international community to support” additional action. Administration officials have made repeated reference to the George W. Bush administration’s inaccurate claims of weapons of mass destruction to justify its 2003 invasion of Iraq.

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Yet even as Obama voiced caution in responding to what he has called the “red line” on chemical weapons, the senior officials described him as ready to move on what one described as the “left-hand side” of a broad spectrum that ranged from “arming the opposition to boots on the ground.”

“We’re clearly on an upward trajectory,” the senior official said. “We’ve moved over to assistance that has a direct military purpose.”

The officials did not specify what U.S. equipment is under consideration, although the rebels have specifically requested ­antitank weapons and surface-to-air missiles.

Syria’s neighbors and, according to recent polls, the American public oppose the insertion of U.S. troops in a conflict that is estimated to have killed more than 70,000 people. Such a move remains highly unlikely barring a spillover of the conflict into major regional instability, significant use of chemical weapons or indications that those weapons are falling into the hands of al-Qaeda-linked Islamist militants fighting alongside Syrian opposition forces.

U.S. and allied military and contract personnel have been training Jordanian and rebel forces to deal with the chemical weapons threat. U.S. intelligence also has tried to contact Syrian government units charged with protecting the weapons to warn against their use, and U.N. experts are preparing to secure chemical sites in the event of a negotiated cease-fire.

But the senior official, one of several who discussed internal administration deliberations on the condition of anonymity, said Obama has “not closed the door to other military actions,” in response to calls from the Syrian opposition and some members of Congress for protection against the Assad government’s ballistic missiles and airstrikes.

No-fly zone concerns

Asked about the possibility of establishing a no-fly zone over rebel-held areas in Syria, the official said the administration was “reviewing all options.”

Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, on Tuesday reiterated his long-held reservations about setting up a no-fly zone, emphasizing that it is more complicated and riskier than advocates believe. “I have to assume . . . that a potential adversary is not just going to sit back” and allow its air defense systems to be destroyed, Dempsey said at a lunch hosted by the Christian Science Monitor.

Syria’s air defenses, located in populated areas in the western part of the country, are “much denser and more sophisticated” than those confronted by the international coalition that intervened in Libya during its 2011 conflict, he said. Establishing a no-fly zone in Syria would require air bases in the region, the positioning of substantial search-and-rescue resources for downed pilots, and the ability to sustain operations for the long term in a time of fiscal constraint and readiness concerns, Dempsey said.

A slow shift in thinking

The administration has been edging toward the provision of weapons to the rebels for several months, first announcing that it would provide nonlethal assistance in the form of food and medical supplies directly to opposition military forces and more recently indicating that it would send defensive gear such as body armor and night-vision goggles.

Since then, several factors have influenced the president’s thinking, according to the officials.

Partner nations, including Jordan, Turkey, Saudi Arabia, Qatar and Britain, have urged the United States — and Obama directly in recent meetings — to take a more active role in helping the Syrian rebels and leading coordination of what has been a somewhat diffuse effort by governments that are providing substantial humanitarian or military aid, or both.

Disputes among those countries, particularly between Qatar and Saudi Arabia, over which rebel military faction to back has led to rising U.S. concern that sophisticated weapons, including ­surface-to-air missiles, are being sent directly to Islamist extremist groups. The administration is not prepared to send missiles, but it believes it can gain more control over others’ supplies if it puts what an official called “more skin in the game” by sending lethal equipment.

Close allies Britain and France also have moved out ahead of the United States with calls for the European Union to drop its arms embargo against Syria and indications that they are prepared to send weaponry to the opposition.

There is waning U.S. hope that the Syrian political opposition would coalesce around a political program and substantive actions on the ground that could persuade the population that it is capable of governing and wean fence-sitters away from supporting Assad.

At the same time, rebel fighters with the U.S.-backed Syrian Free Army led by Gen. Salim Idriss are seen as increasingly cohesive. Idriss, one of the few leaders who is acceptable to both the opposition and its range of international backers, impressed Kerry and other foreign ministers who attended a meeting with the Syrian opposition leaders in Istanbul last weekend and pledged that he would keep weapons out of the hands of extremists.

Kerry was particularly outspoken during closed-door sessions with opposition and international leaders and demanded a more cooperative and integrated effort on all sides, according to participants. That message was amplified by Obama, who met last week with Qatari Emir Hamad bin Khalifa al-Thani and Jordan’s King Abdullah II. In mid-May, he will host Turkish Prime Minister Recep Tayyip Erdogan in Washington.

Karen DeYoung is associate editor and senior national security correspondent for the Washington Post.

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